Couplers can include manual couplers, semi-automatic couplers, and automatic couplers. In particular, there are two main types of coupler used in mechanical “JCB-type” excavators or diggers to couple a digging bucket to a bucket lifting arm:—safety pin types and self-coupling automatic couplers. Couplers are typically hydraulically operated and powered.
Couplers are typically used to connect a tool, such as a digging bucket, to an arm of a utility vehicle for moving and manipulating the tool. Such, arms are often used for lifting. A typical utility vehicle, such as an excavator/digger, which would use a coupler, may have wheels and tyres or tracks, or it may run on rails.
Safety pin type couplers have a disadvantage that is discussed in the following scenario. The operator of a hydraulic digging machine sits in a weatherproof cab and uses the hydraulic arm to dig with a bucket coupled to the end of the arm. If they want to change the bucket for a different bucket or tool they need to get out of the cab, into the cold and rain, pull out the safety pin, get back into the cab and operate the hydraulic arm to de-couple the existing bucket, move the hydraulic arm to an alternative bucket, operate the hydraulic mechanism to couple to the alternative bucket, get out of the cab back into the rain and cold and push through the mechanical safety pin in the-coupling. Then they would have to get back into the cab and use the new bucket.
It has been known for there to be fatal accidents due to the operator of the digger not wanting to spend the time and trouble, and possible discomfort, of getting out of the cab to remove and replace the safety pin. Sometimes users operate the hydraulic digging arm with no safety pin in place. The bucket may stay on the end of the hydraulic arm so long as hydraulic power is still provided. However, if the hydraulic power is impaired, or ceases altogether, the hydraulic fastening of the coupling to the mounting pins on the bucket can become loose, and if there is no safety pin in place the bucket can fall off the arm. It has been known to kill people.
For that reason some people prefer to work with automatic self-locking couplers.
Existing automatic self-locking couplers are known. Examples can be found in the patent publications—U.S. Pat. No. 5,082,389 and U.S. Pat. No. 6,922,926. One type of automatic hydraulic coupler that is known uses a pendulum, or a weighted pivot point, to prevent movement of a hydraulic piston in a “release” direction in the event of failure of hydraulic pressure. It is necessary to angle the arm/bucket to a selected angle of inclination in order to release a coupler that is gravity-biased. Also, these kind of coupler systems use springs to bias components into position. A problem with these couplers is that they are mechanically complex, and there are things that can go wrong. For example, it is possible for cement to form on the springs, or stones to get into the space where a pendulum needs to operate—i.e. components can become jammed and unusable or unreliable. Diggers are, after all, used in rough environments where stones, dirt and concrete exist. Another known hydraulic automatic self-coupling coupler uses a hydraulic ram and an L-shaped pivotable finger to hold a mounting pin in a U-shaped recess. The L-shaped finger pivots down over the previously open mouth of the shaped recess. This coupler has complex pivoting components, capable of being blocked/jammed and not operating properly.
An example of such a device is described in U.S. Pat. No. 5,082,389, which describes a coupler with a spring-biased L-shaped closure member. The coupler has a pair of mutually orientated connective elements, which comprise recesses in the body of the connector. The connective elements are arranged to mount a mounting pin on a tool. The first recess opens substantially downwards and the second recess opens in a direction substantially at right angles to the direction of the opening of the first recess. The first recess has a mouth which is substantially closeable. by the spring biased L-shaped closure member. The closure member is pivoted to an open position by action of a hydraulic piston and cylinder assembly which pivots the closure member away from the mouth of the first recess; a spring returns the L-shaped closure member back to the closed mouth position. Such a device has a disadvantage that the L-shaped closure member is generally weak at retaining the mounting pin of the tool. If the spring or the hydraulic piston and cylinder assembly fails, the closure member may not operate properly and could open under pressure from the mounting pin. This connector also has a disadvantage that it is complex with several moving components which can become clogged with rocks, dirt and cement.